It doesn't even do that well. Algae have short lifespans and when they decompose, the CO2 will go right back into the atmosphere. It's the same reason you can't reasonably capture CO2 with small plants like grasses, nor does the carbon inside you count as captured. The reason trees "capture CO2" is because trees live for a long time and wood decomposes very slowly, and therefore keep its carbon locked in the wood for a long time. The point of capturing carbon is you take it out of circulation for as long as possible.

There are ways to have algae capture carbon, but they are fairly involved (read: very expensive) processes whose scalability is still uncertain. Certainly not a tank in the street.

[–] Flumsy@feddit.de 2 points 9 months ago (1 children)

I was always under the impression that plants chemically convert CO2 and some other stuff to glucose (C6-H12-O6), right? In that case, the algae would still help, wouldnt they?

[–] HiddenLayer5@lemmy.ml 1 points 9 months ago* (last edited 9 months ago)

It helps if and only if the glucose stays as glucose and is not metabolized. Wood is a good application of this, as its cellulose fibers are made of glucose, in a form that is very stable and can stay locked away for a long time (especially if the tree is alive as it does not metabolize the glucose in its own wood and has anti-predation adaptations that actively guard it against other organisms). However, if the glucose decomposes, i.e. is metabolized, it is converted either directly to CO2 or into other compounds that eventually end up as CO2, essentially returning the captured carbon back to the atmosphere.